294 AIR. 



to be the vertical sun, the whole column 

 of air beneath will be heated by the noon- 

 day rays ; that part which the sun has 

 left, will become gradually colder and 

 colder ; and that part to which the sun 

 is approaching, will grow constantly 

 warmer and warmer. 



Q. Then there are THREE qualities of air 

 about this spot ? 



A. Yes \ the air over the place which 

 has passed the meridian is cooling : the 

 air under the vertical sun is the hottest ; 

 and the air which is over the place about 

 to pass under the meridian, is increasing 

 in heat. 



Q. How does this VARIETY in the HEAT of AIR 

 produce WIND ? 



A. The air always seeks to preserve 

 an equilibrium ; so the cold air rushes to 

 the void, made by the upward current of 

 the warmer air. 



Q. Why does not the wind ALWAYS BLOW 

 ONE way, following the direction of the SUN ? 



A. Because the direction of the wind 

 is subject to perpetual interruptions from 

 hills and valleys, deserts and seas. 



